The present invention relates to the field of vibration damping materials and more particularly constrained layer damping materials.
Constrained layer damping materials are required for use in outer space. For example, a constrained layer damping material is utilized between a first and second structural member in order to reduce the transmission of mechanical shock waves or vibrations. An orbiting space station, for example, will be exposed to extreme temperature variations as the vehicle faces the sun and is hidden from the sun as it rotates about the earth. When hidden from the sun, temperatures of -100 degrees F. will be present whereas the vehicle faces the sun, temperatures of plus 160 degrees F. will be present.
The viscoelastic property of such material behaves partially as an elastic rubber band which, after being stretched and released, retracts to its original shape. Such material also acts like a putty which absorbs energy and retains its newly formed shape. The viscoelastic materials combine these two attributes so that although the material returns to its original shape after being stressed, it does so slowly enough to oppose the next cycle of vibration. In other words, such materials have a non-linear response to stress and examination of the stress-strain graph of such material reveals a hysteresis loop, the area of which is a function of energy dissipated as heat for each cycle. Thus, the kinetic energy of vibration is converted into heat, and as a result, vibration is damped. When the applied stress and resulting strain are out of phase with respect to time, Young's modulus is a complex quantity, namely E.sub.1 +iE.sub.2, E.sub.1 representing the elastic modulus and E.sub.2 representing the energy loss modulus. The ratio of E.sub.2 /E.sub.1 defines the well-known loss factor n. Accordingly, the greater the energy conversion into heat, the higher the loss factor and the more effective is the damping material.